Fiberglass batts are well known in the art of insulation and are commonly produced with glass fibers and an aqueous thermosetting resin. The aqueous thermosetting resin is applied on the glass fibers and dried and cured in a forced air oven whereby to bind the fibers together in a batt. Facings such as kraft paper, aluminum foil, etc., are sometimes bonded with a suitable adhesive to the batt after the oven.
One of the disadvantages of this process is that since large volume of air are required to form and cure the batt, it is difficult to control the emission by the binder of toxic gases and aerosols in the air. Furthermore, the heat required to evaporate the water and cure the binder on the batt constitute an expensive means of fabrication.
It is known in the art that cellulosic fibers can provide good insulating properties. To this end, ground recycled paper or virgin pulp are readily available. However, a disadvantage of the use of these products has been the fact that the fibers or bundles of fibers are very short, normally 1 to 10 mm as compared to fiberglass fibers which are in the range of about from 25 to 75 mm. As a result of this short length, a large quantity of liquid binder would be required to bind the fibers together in order to make a cellulosic batt with adequate integrity and this would not be economically feasible. Furthermore, the water used with the binder is undesirable due to the great affinity that the cellulose fibers have to water as compared to fiberglass. This would lead to an increase in the drying time and therefore an increase in the cost. There is therefore a need to find a means to fabricate a batt of cellulosic pulp using an appropriate binder and which could eliminate the problems associated with a liquid binder.
The use of dry binders, such as thermosetting or thermoplastic powders would eliminate the use of water and problems associated therewith. However, these powders must be utilized in large quantities in order to permit the fabrication of batts having an adequate integrity. Such large quantities of binder would not again be economically feasible.
Thermal bonding techniques can be used to bond fibers in a wide variety of nonwoven products such as filters, absorbents and clothing. This process utilizes thermoplastic fibers that bind together with heat. Such fibers will become tacky while preserving their shape at a predetermined temperature. Examples of such fibers are copolymers of vinyl acetate and vinyl chloride which is known under the trade mark WACKER MP FASER and also bicomponents fibers which are known under the trade mark CELBOND. "CELBOND" fibers are fibers manufactured with a high melting point (approximately 240.degree. C.) polyester core and a lower melting point polyester or polyolefin sheath. Several grades are available with sheath melting points in as range of 110.degree. to 200.degree. C.